diff --git a/src/firehose/handlers.ts b/src/firehose/handlers.ts
index 709ec6a..26da928 100644
--- a/src/firehose/handlers.ts
+++ b/src/firehose/handlers.ts
@@ -14,6 +14,7 @@ import {
 	deleteWikiByAtUri,
 	getMemberRole,
 	getNoteByAtUri,
+	getNoteBySlug,
 	getWikiByAtUri,
 	isDidBanned,
 	setWikiTheme,
@@ -228,27 +229,35 @@ export function handleCommitEvent(evt: FirehoseCommit): void {
 	if (typeof record !== "object" || record === null) return;
 	const r = record as Rec;
 
+	const malformed = (): void =>
+		logDrop(atUri, "record is missing required fields");
+
 	switch (evt.collection) {
 		case COLLECTIONS.wiki:
-			if (isWikiRecord(r) && !wikiIsInvalid(atUri, r))
+			if (!isWikiRecord(r)) malformed();
+			else if (!wikiIsInvalid(atUri, r))
 				handleWiki(evt.did, evt.rkey, atUri, r);
 			break;
 		case COLLECTIONS.note:
-			if (isNoteRecord(r) && !noteIsInvalid(atUri, r))
-				handleNote(evt.did, atUri, r);
+			if (!isNoteRecord(r)) malformed();
+			else if (!noteIsInvalid(atUri, r)) handleNote(evt.did, atUri, r);
 			break;
 		case COLLECTIONS.noteRevision:
-			if (isRevisionRecord(r) && !revisionIsInvalid(atUri, r))
-				handleRevision(evt.did, atUri, r);
+			if (!isRevisionRecord(r)) malformed();
+			else if (!revisionIsInvalid(atUri, r)) handleRevision(evt.did, atUri, r);
 			break;
 		case COLLECTIONS.membership:
-			if (isMembershipRecord(r) && !membershipIsInvalid(atUri, r))
+			if (!isMembershipRecord(r)) malformed();
+			else if (!membershipIsInvalid(atUri, r))
 				handleMembership(evt.did, atUri, r);
 			break;
 		case COLLECTIONS.memberRequest:
-			if (isMemberRequestRecord(r)) handleMemberRequest(evt.did, atUri, r);
+			if (!isMemberRequestRecord(r)) malformed();
+			else handleMemberRequest(evt.did, atUri, r);
 			break;
 		case COLLECTIONS.communityBookmark:
+			// Deliberately unlogged: wantedCollections gives us every bookmark on
+			// the network for this NSID, and almost none of them point at a wiki.
 			if (isCommunityBookmarkRecord(r))
 				handleCommunityBookmark(evt.did, atUri, r);
 			break;
@@ -296,7 +305,9 @@ function handleWiki(
 		record.description ?? "",
 	);
 
-	// Known theme name = enforce that preset; anything else falls back to reader mode.
+	// Per the lexicon, a theme present means "render with this", absent means "let
+	// the viewer choose" — so absence is reader mode. The stored theme is reset
+	// too, because nothing reads it outside enforce mode (see theme/apply.ts).
 	const theme = record.theme;
 	if (typeof theme === "string" && theme in themes) {
 		setWikiTheme(did, rkey, "enforce", theme);
@@ -309,15 +320,32 @@ function handleWiki(
 
 function handleNote(did: string, atUri: string, record: NoteRecord): void {
 	const wiki = getWikiByAtUri(record.wikiRef);
-	if (!wiki) return;
-	if (!canDidEditWiki(wiki, did)) return;
+	if (!wiki) {
+		logDrop(atUri, `note.wikiRef unknown: ${record.wikiRef}`);
+		return;
+	}
+	if (!canDidEditWiki(wiki, did)) {
+		logDrop(atUri, `${did} may not edit ${wiki.at_uri}`);
+		return;
+	}
 
 	// Store the NFC form: the same slug written in NFD is a different SQLite key,
 	// so an un-normalized write becomes a note that exists but never resolves.
+	const slug = normalizeSlug(record.slug);
+
+	// upsertNote keys on (wiki_at_uri, slug) and updates only the title, so two
+	// authors picking the same slug would silently merge: the second one's title
+	// on the first one's record. First writer wins, and the loser is reported.
+	const existing = getNoteBySlug(wiki.at_uri, slug);
+	if (existing && existing.at_uri !== atUri) {
+		logDrop(atUri, `note.slug "${slug}" already taken by ${existing.at_uri}`);
+		return;
+	}
+
 	upsertNote(
 		wiki.at_uri,
 		wiki.slug,
-		normalizeSlug(record.slug),
+		slug,
 		record.title,
 		did,
 		atUri,
@@ -333,10 +361,19 @@ function handleRevision(
 	record: RevisionRecord,
 ): void {
 	const note = getNoteByAtUri(record.noteRef);
-	if (!note) return;
+	if (!note) {
+		logDrop(atUri, `revision.noteRef unknown: ${record.noteRef}`);
+		return;
+	}
 	const wiki = getWikiByAtUri(note.wiki_at_uri);
-	if (!wiki) return;
-	if (!canDidEditWiki(wiki, did)) return;
+	if (!wiki) {
+		logDrop(atUri, `note's wiki unknown: ${note.wiki_at_uri}`);
+		return;
+	}
+	if (!canDidEditWiki(wiki, did)) {
+		logDrop(atUri, `${did} may not edit ${wiki.at_uri}`);
+		return;
+	}
 
 	applyRevisionFromFirehose(
 		note.at_uri,
@@ -359,9 +396,15 @@ function handleMembership(
 	record: MembershipRecord,
 ): void {
 	const wiki = getWikiByAtUri(record.wikiRef);
-	if (!wiki) return;
+	if (!wiki) {
+		logDrop(atUri, `membership.wikiRef unknown: ${record.wikiRef}`);
+		return;
+	}
 
-	if (wiki.did !== did) return;
+	if (wiki.did !== did) {
+		logDrop(atUri, `only ${wiki.did} may grant membership to its wiki`);
+		return;
+	}
 
 	upsertMembership(
 		wiki.at_uri,
@@ -379,7 +422,10 @@ function handleMemberRequest(
 	record: MemberRequestRecord,
 ): void {
 	const wiki = getWikiByAtUri(record.wikiRef);
-	if (!wiki) return;
+	if (!wiki) {
+		logDrop(atUri, `memberRequest.wikiRef unknown: ${record.wikiRef}`);
+		return;
+	}
 
 	upsertRequest(wiki.at_uri, wiki.slug, did, atUri, record.createdAt);
 }